Precision features may be fabricated on semiconductor wafers such as GaAs, InP, and the like through formation of oxide layers. Of particular interest are such applications for manufacture of vertical cavity surface emitting lasers (VCSELs). The prior art has employed wet oxidation in conjunction with calibrated oxidation rates and directly observed optical monitoring of the wafer within an oxidation furnace where temperature and humidity are controlled. One typical example of prior art is described by Feld, et al, IEEE Photonics Technology Letters, vol. 10, no. 2, February 1998 wherein the oxidation furnace includes a chamber featuring an internally disposed heat source in proximity to a chuck supporting the wafer. A mass flow controlled vapor source is arranged to introduce the vapor into the chamber, at approximately atmospheric pressure. A microscope views the oxidation site of the wafer. Oxidation rates of the order μm/min are realized and the process is terminated under manual control of the vapor source.
Controlling the final aperture size may be achieved, if so desired, by direct control of oxidation time, based on prior calibration. Because of wafer to wafer variations, manufacturers presently prefer to view the formation of the aperture in-situ during oxidation and to stop the process once it has been determined that the desired aperture size has been reached.
It would thus be desirable to provide a system and method that tries to optimizes the oxidation process while maintaining in-situ monitoring capability.